Conventional air cleaners, such as filtration air cleaners (FACS) remove particles from the air by trapping the particles in filters. Other air cleaners, such as electrostatic precipitation air cleaners (ESPACs), remove particles from the air by collecting the particles on electrically charged collection surfaces, usually one or more metallic plates coupled to high voltages. Once full of captured particles, the filters or plates may then be disposed of, washed or replaced, thereby necessitating convenient and safe access to the filters or plates.
FACs suffer from several drawbacks including a marked drop-off of air flow as the filter becomes increasingly blocked with collected particles; the need for a powerful fan due to the significant pressure drop across the filter (powerful fans also tend to generate more noise and consume more power than less powerful fans); and the need to periodically replace the filter.
Some of the drawbacks of FACs are overcome by ESPACs. Because ESPACs can operate with a lower pressure drop, ESPACs can operate with lower power fans, thereby reducing the noise generated as well as the power consumed. In addition, the collection plates of ESPACs can be washed or wiped clean of particles and re-used repeatedly without replacement.
ESPACs, however, require shielding to protect users from the high voltages (e.g., several kilovolts) that are applied to the metal collecting plates. Even after the power supply has been switched off, there is the danger of shock from electrical charges stored on the plates. In order to safely remove the collecting plates for cleaning, an interlock mechanism is often provided to automatically discharge the plates before they can be accessed by the user. Furthermore, electrical breakdown and leakage between the metal plates will cause a loss of efficiency and generate ozone. Increasing the spacing between the plates will reduce electrical breakdown in the air but will also reduce efficiency.
U.S. Pat. No. 6,749,669 (hereinafter the “'669 patent”) addresses some of the shortcomings of conventional ESPACs. The '669 patent describes a particle precipitation device for removing particles entrained in air comprising an array of passages through which the air can pass relatively freely. The passages are provided between sheets of electrically conductive material to which are applied high and low electrical potentials alternately to provide charged sites in the array for collecting particles from the air passing therethrough. A fan is provided to create the air flow through the passages. The passages are preferably provided by sheets of fluted plastic preferably having conductive material on opposite external faces thereof. The fluted plastic sheets may, for example, be overlaid one on top of the other, folded in concertina fashion, formed into a spiral, or formed in an array of concentric sheets arranged in circles.
The '669 patent also describes the use of electrodes comprised of high impedance electrically conductive materials for applying the electrical potentials across the air passages. Unlike low impedance, metallic plates, such high impedance electrodes restrict current flow, thereby reducing the shock hazard to users.